339. Ratio Of Gears

Description

339. Ratio Of Gears

Suppose we have two shafts, Dand F, as shown in Fig. 153 and that we want to connect these shafts by gears so that shaft D will make one revolution while shaft F makes two.

In order to do this we must place a gear on shaft D having twice the number of teeth of the gear on shaft F. If we put a gear on D with 24 teeth, the gear on F will then have 12 teeth, or half as many, and each time the gear on D turns around once the gear on F will turn twice; that is, the 24 teeth on gear D will have to turn gear F twice in order to mesh with 12 teeth on F.

The relation of the speed of F to the speed of D is 2 to 1. This is called the ratio of the gearing. We can now write the ratios between the speeds and the number of teeth in the form of a proportion thus: 24 :12 =2:1, that is, the number of teeth on gear D is to the number of teeth on gear F as the speed of F is to the speed of D.